This invention relates generally to thin film deposition methods and apparatuses and, more particularly, to methods and apparatuses for the production of unsupported thin film particles.
Unsupported thin film particles, such as metallic flakes or flakes of a multi-layer thin film composite, are in high demand for a wide variety of products. In coating products (such as paints and inks), for example, thin film particles can be used to impart unique optical, mechanical and electrical properties to the coating product. Thin film coating particles are also commonly incorporated into sheet products (such as plastic films) and into cast and molded products to give such products unique optical, mechanical or electrical properties.
Thin film coating particles are substantially two-dimensional with matching upper and lower surfaces. The thicknesses of such particles are usually less than 10 microns, most usually less than 1 micron. Depending upon the intended use of the particles, the upper and lower surfaces of the particles typically have lateral dimensions between about 5 microns and about 500 microns.
The most common typical prior art method of producing unsupported thin film particles requires that thin film layers be deposited onto a moving web. The web is thereafter soaked in a solvent solution wherein the thin film flakes are separated from the web. This prior art method of producing unsupported thin film particles, however, has not been wholly satisfactory. For one thing, the process cannot be made wholly continuous, because the movement of the web must periodically be halted so that the web can be soaked in solvent solution for some appreciable time. This markedly limits products capacity. Also, the necessity of using a web represents a considerable capital and maintenance cost. This is especially true because the web must frequently be replaced. Finally, in those embodiments where a chilled moving surface is desirable, the use of a web generally requires multiple rotating chill drums. This is because, for a given web tension, the contact force (and hence the effectively cooled contact area) between the web and each chill drum is inversely proportional to the diameter of each chill drum. The requirement of multiple chill drums, however, requires large housings. Such large housingsxe2x80x94which must typically be operated under vacuumxe2x80x94necessarily results in increased capital and operating expenses.
Accordingly, there is a need for a simple, efficient and inexpensive method of producing unsupported thin film particles which avoids the above-listed problems in the prior art.
The invention satisfies this need. The invention is a method for the production of unsupported thin film composite particles comprising the steps of: (a) depositing a surface coating onto a moving surface; (b) depositing at least one thin film layer onto the surface coating to provide a thin film structure disposed atop the surface coating; and (c) scraping the thin film structure from the surface coating. The invention is also a unique apparatus for carrying out this method.
The surface coating is typically a wax and the thin film is typically scraped from the surface coating by a knife blade disposed proximate to the surface of the moving surface.
In a typical embodiment, the moving surface is a rotatable metallic drum disposed within a vacuum chamber. Located about the periphery of the drum is a plurality of coating material applicators, each adapted to distribute a single coating material onto the surface of the rotating drum. Preferably, each coating material applicator is disposed in a separate subcompartment within the vacuum chamber.
After the thin film structure (now in flake form) is scraped from the surface coating, residual surface coating material is removed from the structure, typically in a solvent washing process. The surface coating material can then be recycled to the vacuum chamber for redeposition onto the rotatable drum.